The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory captions and links exemplifying features within the Earth system. The community is invited to contribute digital imagery, short captions and relevant links.

Puddle Ice Crystal Structure

The photo above was taken in Red Deer, Alberta, Canada on April 12, 2007. When the remnants of the winter snow pack finally melt, numerous small puddles form in parking lots or anywhere there's a slight depression. On the night prior to when this picture was snapped, the temperature dropped slowly to a low of -3°C (28 degrees F). This relatively “warm” temperature, along with accumulated heat from the ground, allowed the water to freeze very slowly. The result was a layer of ice only 2 mm (0.8 in) thick and this lovely large ice crystal structure in the puddle. Freezing would have occurred from the shallower edges of the puddle towards the middle. Some form of obstruction or nucleus, such as a small pebble, probably formed a starting point for the crystal structure, which expanded by essentially growing on itself. The concentric triangles on the right would have been the last part to freeze. Shown are two AA batteries for scale. The entire crystal structure was about 80 cm (31 in) long and 45 cm (18 in) wide, at the top of the “Y.” The photo was taken at 8:00 a.m. (local time) at a relatively low angle towards the Sun in order to improve the visibility of the crystal structure.